1. Field of the Invention
The present invention relates to a method for manufacturing a suture needle for medical use, and particularly, to a method for manufacturing a fine eyeless suture needle having a needle diameter less than 150 micrometers.
2. Background of the Invention
In a surgical eyeless suture needle, a hole of a predetermined depth is formed in the end surface on a base side along the axial center, and the end of a suture thread is inserted into the hole and set by caulking in the suture needle.
As the hole machining methods of the surgical eyeless suture needle, methods, such as drilling, electrical discharge machining, and laser beam machining, are conventionally used.
In the case of the drilling and the electrical discharge machining, a drill and a discharge electrode having the same diameter as a hole diameter are used. Therefore, if a needle diameter is reduced, it is necessary to reduce the diameter of the drill, and the diameter of the electrode in accordance with the needle diameter. In the case of a small needle diameter equal to or less than 0.3 mm, a drill and an electrode thinner than the needle diameter are required, and the manufacturing thereof becomes difficult.
On the other hand, in the case of the laser beam machining, tools, such as the drill and the electrode, are not required at all, and an extremely small hole can be formed. According to this machining method, a portion serving as the hole of a needle material is instantaneously heated with the energy of laser beams, and sublimated to form a hole.
However, the hole formation machining of the eyeless suture needle, and in particular hole formation machining for an eyeless suture needle having extremely small needle diameter less than 150 micrometers, poses various problems compared with other general laser beam machining.
For example, when a hole of a diameter of 60 micrometers is formed in a needle material having a needle diameter of 100 micrometers, the thickness of the hole wall is only 20 micrometers. The depth of the hole is required to be 8 to 15 times as large as the hole diameter. When the hole diameter is 60 micrometers, the depth of the hole is 480 to 900 micrometers. The hole must not be a pierced hole visible from the outside, but a dead-end hole not seen from the outside except an entrance.
Accordingly, when a hole is formed in a suture needle having a needle diameter less than 150 micrometers, it is extremely difficult to keep the diameter, depth, and shape of the hole constant, and the suture needle of the above size is not manufactured by other manufacturers, or a hole part is lengthened in a plate shape and caulked so as to wrap the suture thread. However, according to this method, since the caulked part is long and stepped, and further, the caulking is performed by force, an opened line is formed on a boundary line between the caulked portion of the needle material where the suture thread is fixed and the anterior portion, which opened line easily causes damage to body tissues. In the case of the laser beam machining, a material sublimated by laser beams must be dispersed outside the hole. However, there occurs sometimes a so-called sputtering phenomenon that the material which is not dispersed adheres to the inner wall of the hole and solidifies, and the material fills the hole, which makes insertion of the suture thread difficult.
FIGS. 5A, B, and C are examples of defective hole formation, wherein FIG. 5A shows an example of hole bending, FIG. 5B shows an example of a pierced hole, and FIG. 5C shows an example of hole rupture. In the case of the hole bending of FIG. 5A, a suture thread cannot be inserted into the inner part of the hole, and a suture thread of sufficient length cannot fixed by caulking. Moreover, there is a part where the inner wall became thin, and the part may be torn before use. The pierced hole of FIG. 5B shows a state where a side part of the inner part of the hole has melted and opened, and the hole rupture of FIG. 5C shows a state where a side part has melted and been lost from the entrance portion to the inner part of the hole. The suture thread cannot be fixed by caulking in the cases of FIGS. 5B and 5C. Since the suture thread is exposed from caulked holes, even if the suture thread can be fixed by caulking, the suture thread cannot smoothly pass through body tissues. The following is known as a cause of such defective hole formation.
When a hole diameter is large compared with a needle diameter, the outside thickness of the hole is greatly deflected and one side becomes thin even when the center of the hole is shifted only slightly from the center of a needle material. When laser beams are radiated, temperature at the thin part rapidly rises, the thin part melts, and the hole bending, the pierced hole, the hole rupture, or the like occurs.
When the needle diameter is reduced, the ratio of the hole diameter increases, the inner wall becomes thin, and the above-mentioned phenomenon tends to occur. When the needle diameter becomes small, the laser beam irradiation of even only one pulse is excessive, and the entire base end part may be melted and lost.
In view of the above instances, a patent document 1 (JP. A. 1988-140789) proposes a method for keeping the diameter, depth, and shape of a hole constant. This is a method for forming the hole by providing an electric shutter opened and closed by electric signals between a laser oscillator and the base end part of a suture needle, cutting the rising edge portion and falling edge portion of the output of a laser beam, and transmitting only the stable middle portion of the laser beam. According to this method, strength of the laser beam radiated to the base end part of the suture needle can be kept constant since only the stabilized portion among the pulses of the laser beam is used. As a result, satisfactory hole formation without the hole bending, the pierced hole, and the hole rupture is achieved for an eyeless suture needle having a needle diameter of approximately 300 micrometers. Moreover, hole clogging due to sputtering can also be prevented.
However, when the needle diameter is thinner than 150 micrometers, no satisfactory hole could be formed according to the hole formation by the laser beam and electric shutter of the above patent document 1. This is caused by the outside thickness of the hole becoming thin since the needle diameter becomes small, and heat capacity is reduced. Since the heat capacity of the outside of the hole is reduced, a pierced hole having a melted and lost wall tends to be produced even when the hole is formed, or sputtering occurs and the hole tends to be clogged. Therefore, no satisfactory hole could be formed by the method using only the stabilized portion among the pulses of the laser beam as described in the patent document 1.
If the optical axis of the laser beam is not coincident with the center of the end surface of the needle material as mentioned above, the wall melts due to decentering, which causes the pierced hole. Therefore, the laser beam machining is performed by using a machining laser beam after confirmation of the position of the end surface of a needle material with a microscope or the like while using visible laser beams, and then positioning. However, the stability of the output of the laser beam is adversely affected when an optical element is in the optical path of the machining laser beam.
Accordingly, a patent document 2 (JP. A. 1988-171235) aims at the stabilization of the output of a laser beam by adopting a configuration of placing a needle material on one side of a machining laser oscillator, providing a visible laser oscillator on the other side, and without providing any optical element of the visible laser oscillator in the optical path of a machining laser beam.